>>PS Also try -b:256 or -b:1024 instead of -b:200...
> Why 256 or 1024? I'll do it, but I would simply like to understand this choice of numbers.

As Janne already mentioned, computers like numbers that are powers of two.
In this case, the OSS audio API (the /dev/dsp input/outputs), requires
the buffer to be a power of two. You can give other numbers in -b:xxx,
but the result will be round to the nearest power.